Stop creation of 'None' cache directory

[krisgesling]

Description

The persistent_cache_dir is assigned None if no preloaded_cache exists.
None was then created as a directory when it's clearly not needed.

Re-ordered slightly to keep all the directory setting and checking together.

Fixes #2930
Thanks to @JarbasAI for the fix

How to test

1. Set TTS.module to mimic which has no default preloaded cache directory
2. Launch Mycroft
3. See that a mycroft-core/None directory is created.
4. Delete this directory, then apply this PR and repeat.

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[devops-mycroft]

Voight Kampff Integration Test Succeeded (Results)

[codecov-commenter]

Codecov Report

Merging #2931 (21eabce) into dev (8fa6508) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##              dev    #2931      +/-   ##
==========================================
- Coverage   52.62%   52.61%   -0.01%     
==========================================
  Files         123      123              
  Lines       11016    11016              
==========================================
- Hits         5797     5796       -1     
- Misses       5219     5220       +1     

Impacted Files	Coverage Δ
mycroft/tts/cache.py	83.12% <100.00%> (ø)
mycroft/client/speech/listener.py	48.04% <0.00%> (-0.36%)	⬇️

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[forslund]

Works great, no more None directory :)